1 // SPDX-License-Identifier: GPL-2.0-only
3 * Copyright (C) 2020 - Google LLC
4 * Author: David Brazdil <dbrazdil@google.com>
6 * Generates relocation information used by the kernel to convert
7 * absolute addresses in hyp data from kernel VAs to hyp VAs.
9 * This is necessary because hyp code is linked into the same binary
10 * as the kernel but executes under different memory mappings.
11 * If the compiler used absolute addressing, those addresses need to
12 * be converted before they are used by hyp code.
14 * The input of this program is the relocatable ELF object containing
15 * all hyp code/data, not yet linked into vmlinux. Hyp section names
16 * should have been prefixed with `.hyp` at this point.
18 * The output (printed to stdout) is an assembly file containing
19 * an array of 32-bit integers and static relocations that instruct
20 * the linker of `vmlinux` to populate the array entries with offsets
21 * to positions in the kernel binary containing VAs used by hyp code.
23 * Note that dynamic relocations could be used for the same purpose.
24 * However, those are only generated if CONFIG_RELOCATABLE=y.
36 #include <sys/types.h>
40 #include <generated/autoconf.h>
42 #define HYP_SECTION_PREFIX ".hyp"
43 #define HYP_RELOC_SECTION ".hyp.reloc"
44 #define HYP_SECTION_SYMBOL_PREFIX "__hyp_section_"
47 * AArch64 relocation type constants.
48 * Included in case these are not defined in the host toolchain.
50 #ifndef R_AARCH64_ABS64
51 #define R_AARCH64_ABS64 257
53 #ifndef R_AARCH64_LD_PREL_LO19
54 #define R_AARCH64_LD_PREL_LO19 273
56 #ifndef R_AARCH64_ADR_PREL_LO21
57 #define R_AARCH64_ADR_PREL_LO21 274
59 #ifndef R_AARCH64_ADR_PREL_PG_HI21
60 #define R_AARCH64_ADR_PREL_PG_HI21 275
62 #ifndef R_AARCH64_ADR_PREL_PG_HI21_NC
63 #define R_AARCH64_ADR_PREL_PG_HI21_NC 276
65 #ifndef R_AARCH64_ADD_ABS_LO12_NC
66 #define R_AARCH64_ADD_ABS_LO12_NC 277
68 #ifndef R_AARCH64_LDST8_ABS_LO12_NC
69 #define R_AARCH64_LDST8_ABS_LO12_NC 278
71 #ifndef R_AARCH64_TSTBR14
72 #define R_AARCH64_TSTBR14 279
74 #ifndef R_AARCH64_CONDBR19
75 #define R_AARCH64_CONDBR19 280
77 #ifndef R_AARCH64_JUMP26
78 #define R_AARCH64_JUMP26 282
80 #ifndef R_AARCH64_CALL26
81 #define R_AARCH64_CALL26 283
83 #ifndef R_AARCH64_LDST16_ABS_LO12_NC
84 #define R_AARCH64_LDST16_ABS_LO12_NC 284
86 #ifndef R_AARCH64_LDST32_ABS_LO12_NC
87 #define R_AARCH64_LDST32_ABS_LO12_NC 285
89 #ifndef R_AARCH64_LDST64_ABS_LO12_NC
90 #define R_AARCH64_LDST64_ABS_LO12_NC 286
92 #ifndef R_AARCH64_MOVW_PREL_G0
93 #define R_AARCH64_MOVW_PREL_G0 287
95 #ifndef R_AARCH64_MOVW_PREL_G0_NC
96 #define R_AARCH64_MOVW_PREL_G0_NC 288
98 #ifndef R_AARCH64_MOVW_PREL_G1
99 #define R_AARCH64_MOVW_PREL_G1 289
101 #ifndef R_AARCH64_MOVW_PREL_G1_NC
102 #define R_AARCH64_MOVW_PREL_G1_NC 290
104 #ifndef R_AARCH64_MOVW_PREL_G2
105 #define R_AARCH64_MOVW_PREL_G2 291
107 #ifndef R_AARCH64_MOVW_PREL_G2_NC
108 #define R_AARCH64_MOVW_PREL_G2_NC 292
110 #ifndef R_AARCH64_MOVW_PREL_G3
111 #define R_AARCH64_MOVW_PREL_G3 293
113 #ifndef R_AARCH64_LDST128_ABS_LO12_NC
114 #define R_AARCH64_LDST128_ABS_LO12_NC 299
117 /* Global state of the processed ELF. */
123 Elf64_Shdr *sh_table;
124 const char *sh_string;
127 #if defined(CONFIG_CPU_LITTLE_ENDIAN)
129 #define elf16toh(x) le16toh(x)
130 #define elf32toh(x) le32toh(x)
131 #define elf64toh(x) le64toh(x)
133 #define ELFENDIAN ELFDATA2LSB
135 #elif defined(CONFIG_CPU_BIG_ENDIAN)
137 #define elf16toh(x) be16toh(x)
138 #define elf32toh(x) be32toh(x)
139 #define elf64toh(x) be64toh(x)
141 #define ELFENDIAN ELFDATA2MSB
145 #error PDP-endian sadly unsupported...
149 #define fatal_error(fmt, ...) \
151 fprintf(stderr, "error: %s: " fmt "\n", \
152 elf.path, ## __VA_ARGS__); \
153 exit(EXIT_FAILURE); \
154 __builtin_unreachable(); \
157 #define fatal_perror(msg) \
159 fprintf(stderr, "error: %s: " msg ": %s\n", \
160 elf.path, strerror(errno)); \
161 exit(EXIT_FAILURE); \
162 __builtin_unreachable(); \
165 #define assert_op(lhs, rhs, fmt, op) \
167 typeof(lhs) _lhs = (lhs); \
168 typeof(rhs) _rhs = (rhs); \
170 if (!(_lhs op _rhs)) { \
171 fatal_error("assertion " #lhs " " #op " " #rhs \
172 " failed (lhs=" fmt ", rhs=" fmt \
173 ", line=%d)", _lhs, _rhs, __LINE__); \
177 #define assert_eq(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, ==)
178 #define assert_ne(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, !=)
179 #define assert_lt(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, <)
180 #define assert_ge(lhs, rhs, fmt) assert_op(lhs, rhs, fmt, >=)
183 * Return a pointer of a given type at a given offset from
184 * the beginning of the ELF file.
186 #define elf_ptr(type, off) ((type *)(elf.begin + (off)))
188 /* Iterate over all sections in the ELF. */
189 #define for_each_section(var) \
190 for (var = elf.sh_table; var < elf.sh_table + elf16toh(elf.ehdr->e_shnum); ++var)
192 /* Iterate over all Elf64_Rela relocations in a given section. */
193 #define for_each_rela(shdr, var) \
194 for (var = elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset)); \
195 var < elf_ptr(Elf64_Rela, elf64toh(shdr->sh_offset) + elf64toh(shdr->sh_size)); var++)
197 /* True if a string starts with a given prefix. */
198 static inline bool starts_with(const char *str, const char *prefix)
200 return memcmp(str, prefix, strlen(prefix)) == 0;
203 /* Returns a string containing the name of a given section. */
204 static inline const char *section_name(Elf64_Shdr *shdr)
206 return elf.sh_string + elf32toh(shdr->sh_name);
209 /* Returns a pointer to the first byte of section data. */
210 static inline const char *section_begin(Elf64_Shdr *shdr)
212 return elf_ptr(char, elf64toh(shdr->sh_offset));
215 /* Find a section by its offset from the beginning of the file. */
216 static inline Elf64_Shdr *section_by_off(Elf64_Off off)
218 assert_ne(off, 0UL, "%lu");
219 return elf_ptr(Elf64_Shdr, off);
222 /* Find a section by its index. */
223 static inline Elf64_Shdr *section_by_idx(uint16_t idx)
225 assert_ne(idx, SHN_UNDEF, "%u");
226 return &elf.sh_table[idx];
230 * Memory-map the given ELF file, perform sanity checks, and
231 * populate global state.
233 static void init_elf(const char *path)
238 /* Store path in the global struct for error printing. */
241 /* Open the ELF file. */
242 fd = open(path, O_RDONLY);
244 fatal_perror("Could not open ELF file");
246 /* Get status of ELF file to obtain its size. */
247 ret = fstat(fd, &stat);
250 fatal_perror("Could not get status of ELF file");
253 /* mmap() the entire ELF file read-only at an arbitrary address. */
254 elf.begin = mmap(0, stat.st_size, PROT_READ, MAP_PRIVATE, fd, 0);
255 if (elf.begin == MAP_FAILED) {
257 fatal_perror("Could not mmap ELF file");
260 /* mmap() was successful, close the FD. */
263 /* Get pointer to the ELF header. */
264 assert_ge(stat.st_size, sizeof(*elf.ehdr), "%lu");
265 elf.ehdr = elf_ptr(Elf64_Ehdr, 0);
267 /* Check the ELF magic. */
268 assert_eq(elf.ehdr->e_ident[EI_MAG0], ELFMAG0, "0x%x");
269 assert_eq(elf.ehdr->e_ident[EI_MAG1], ELFMAG1, "0x%x");
270 assert_eq(elf.ehdr->e_ident[EI_MAG2], ELFMAG2, "0x%x");
271 assert_eq(elf.ehdr->e_ident[EI_MAG3], ELFMAG3, "0x%x");
273 /* Sanity check that this is an ELF64 relocatable object for AArch64. */
274 assert_eq(elf.ehdr->e_ident[EI_CLASS], ELFCLASS64, "%u");
275 assert_eq(elf.ehdr->e_ident[EI_DATA], ELFENDIAN, "%u");
276 assert_eq(elf16toh(elf.ehdr->e_type), ET_REL, "%u");
277 assert_eq(elf16toh(elf.ehdr->e_machine), EM_AARCH64, "%u");
279 /* Populate fields of the global struct. */
280 elf.sh_table = section_by_off(elf64toh(elf.ehdr->e_shoff));
281 elf.sh_string = section_begin(section_by_idx(elf16toh(elf.ehdr->e_shstrndx)));
284 /* Print the prologue of the output ASM file. */
285 static void emit_prologue(void)
288 ".pushsection " HYP_RELOC_SECTION ", \"a\"\n");
291 /* Print ASM statements needed as a prologue to a processed hyp section. */
292 static void emit_section_prologue(const char *sh_orig_name)
294 /* Declare the hyp section symbol. */
295 printf(".global %s%s\n", HYP_SECTION_SYMBOL_PREFIX, sh_orig_name);
299 * Print ASM statements to create a hyp relocation entry for a given
300 * R_AARCH64_ABS64 relocation.
302 * The linker of vmlinux will populate the position given by `rela` with
303 * an absolute 64-bit kernel VA. If the kernel is relocatable, it will
304 * also generate a dynamic relocation entry so that the kernel can shift
305 * the address at runtime for KASLR.
307 * Emit a 32-bit offset from the current address to the position given
308 * by `rela`. This way the kernel can iterate over all kernel VAs used
309 * by hyp at runtime and convert them to hyp VAs. However, that offset
310 * will not be known until linking of `vmlinux`, so emit a PREL32
311 * relocation referencing a symbol that the hyp linker script put at
312 * the beginning of the relocated section + the offset from `rela`.
314 static void emit_rela_abs64(Elf64_Rela *rela, const char *sh_orig_name)
316 /* Offset of this reloc from the beginning of HYP_RELOC_SECTION. */
317 static size_t reloc_offset;
319 /* Create storage for the 32-bit offset. */
323 * Create a PREL32 relocation which instructs the linker of `vmlinux`
324 * to insert offset to position <base> + <offset>, where <base> is
325 * a symbol at the beginning of the relocated section, and <offset>
326 * is `rela->r_offset`.
328 printf(".reloc %lu, R_AARCH64_PREL32, %s%s + 0x%lx\n",
329 reloc_offset, HYP_SECTION_SYMBOL_PREFIX, sh_orig_name,
330 elf64toh(rela->r_offset));
335 /* Print the epilogue of the output ASM file. */
336 static void emit_epilogue(void)
338 printf(".popsection\n");
342 * Iterate over all RELA relocations in a given section and emit
343 * hyp relocation data for all absolute addresses in hyp code/data.
345 * Static relocations that generate PC-relative-addressing are ignored.
346 * Failure is reported for unexpected relocation types.
348 static void emit_rela_section(Elf64_Shdr *sh_rela)
350 Elf64_Shdr *sh_orig = &elf.sh_table[elf32toh(sh_rela->sh_info)];
351 const char *sh_orig_name = section_name(sh_orig);
354 /* Skip all non-hyp sections. */
355 if (!starts_with(sh_orig_name, HYP_SECTION_PREFIX))
358 emit_section_prologue(sh_orig_name);
360 for_each_rela(sh_rela, rela) {
361 uint32_t type = (uint32_t)elf64toh(rela->r_info);
363 /* Check that rela points inside the relocated section. */
364 assert_lt(elf64toh(rela->r_offset), elf64toh(sh_orig->sh_size), "0x%lx");
368 * Data relocations to generate absolute addressing.
369 * Emit a hyp relocation.
371 case R_AARCH64_ABS64:
372 emit_rela_abs64(rela, sh_orig_name);
374 /* Allow relocations to generate PC-relative addressing. */
375 case R_AARCH64_LD_PREL_LO19:
376 case R_AARCH64_ADR_PREL_LO21:
377 case R_AARCH64_ADR_PREL_PG_HI21:
378 case R_AARCH64_ADR_PREL_PG_HI21_NC:
379 case R_AARCH64_ADD_ABS_LO12_NC:
380 case R_AARCH64_LDST8_ABS_LO12_NC:
381 case R_AARCH64_LDST16_ABS_LO12_NC:
382 case R_AARCH64_LDST32_ABS_LO12_NC:
383 case R_AARCH64_LDST64_ABS_LO12_NC:
384 case R_AARCH64_LDST128_ABS_LO12_NC:
386 /* Allow relative relocations for control-flow instructions. */
387 case R_AARCH64_TSTBR14:
388 case R_AARCH64_CONDBR19:
389 case R_AARCH64_JUMP26:
390 case R_AARCH64_CALL26:
392 /* Allow group relocations to create PC-relative offset inline. */
393 case R_AARCH64_MOVW_PREL_G0:
394 case R_AARCH64_MOVW_PREL_G0_NC:
395 case R_AARCH64_MOVW_PREL_G1:
396 case R_AARCH64_MOVW_PREL_G1_NC:
397 case R_AARCH64_MOVW_PREL_G2:
398 case R_AARCH64_MOVW_PREL_G2_NC:
399 case R_AARCH64_MOVW_PREL_G3:
402 fatal_error("Unexpected RELA type %u", type);
407 /* Iterate over all sections and emit hyp relocation data for RELA sections. */
408 static void emit_all_relocs(void)
412 for_each_section(shdr) {
413 switch (elf32toh(shdr->sh_type)) {
415 fatal_error("Unexpected SHT_REL section \"%s\"",
418 emit_rela_section(shdr);
424 int main(int argc, const char **argv)
427 fprintf(stderr, "Usage: %s <elf_input>\n", argv[0]);